Solar resource assessment study for Pakistan

Solar resource assessment becomes a very important factor for planners of Photovoltaic (PV) and Concentrated Solar Power (CSP) systems. Choice between nearby locations can make a difference if a plant is profitable or not, especially in a climatic region with complex topography as can be found in Pakistan. Nevertheless, Pakistan’s geographic location and climate offers a very high potential for solar energy applications. The solar resource assessment study presented in this article describes the approach and set-up required by the World Bank’s Energy Sector Management Assistance Program (ESMAP).1 The project aims to create a validated solar atlas for Pakistan based on a combination of satellite data and ground measurements to support country-driven efforts to improve renewable energy resource awareness and exploitation. There are several country-specific, ESMAP-funded projects conducted by the World Bank Group (WBG) that cover comprehensive mapping and geospatial planning, including ground-based data collection. The solar resource estimation of Pakistan was one of the first projects to be approved within the program. The final and validated dataset ultimately will be published in the International Renewable Energy Agencies’ (IRENA) global atlas for renewable energy

Growth factor regulation of uncoupling protein-1 mRNA expression in brown adipocytes

9 pages, 7 figures.To study the effect of the mitogens epidermal growth factor (EGF), acidic and basic fibroblast growth factors (aFGF and bFGF), and vasopressin on brown adipocyte differentiation, we analyzed the expression of uncoupling protein-1 (UCP-1) mRNA. Quiescent brown preadipocytes express high levels of UCP-1 mRNA in response to triiodothyronine (T3) and norepinephrine (NE). The addition of serum or the mitogenic condition aFGF + vasopressin + NE or EGF + vasopressin + NE decreases UCP-1 mRNA. A second addition of mitogens further decreases UCP-1 mRNA. Treatment with aFGF or bFGF alone increases UCP-1 mRNA, whereas the addition of EGF or vasopressin dramatically reduces UCP-1 mRNA levels. The continuous presence of T3 increases UCP-1 mRNA levels in cells treated with EGF, aFGF, or bFGF. The effect of T3 on the stimulation of DNA synthesis also was tested. T3 inhibits the mitogenic activity of aFGF and bFGF. In conclusion, mitogens like aFGF or bFGF allow brown adipocyte differentiation, whereas EGF and vasopressin inhibit the differentiation process. T3 behaves as an important hormone that regulates both brown adipocyte proliferation and differentiation.This work was supported by Dirección General de Investigación Científica y Técnica Grants PB 92-0061 and PB 95-0097, Comunidad Autónoma de Madrid Grant CAM 08.8/0030/98, and Fondo de Investigaciones Sanitarias de la Seguridad Social Grants FISS 94/0274 and FISS 99/0813 (Spain). B. García was recipient of a fellowship from the Spanish Ministerio de Educación y Cultura.Peer reviewe

Best Practices for Solar Irradiance Measurements with Rotating Shadowband Irradiometers

Large-scale solar plant projects require diligent solar resource assessments. For concentrating solar technologies the focus of the resource assessment lies on direct beam irradiation. Unfortunately, high accuracy irradiance data are scarcely available in regions which are attractive for solar energy applications. Satellite data can only be used in combination with ground data to estimate inter-annual variability and long-term mean values. Hence, new ground measurements have to be collected for solar plant projects. Ground measurement data usually show significantly higher accuracies than satellite derived irradiance data, when general guidelines regarding site selection and preparation, instrument selection and maintenance and data quality monitoring are respected. These best practices for Rotating Shadowband Irradiometers (RSIs) are presented in this document. Appropriate irradiance sensors for ground measurements must be selected in consideration of general surrounding conditions for equipment and maintenance to gain and maintain the necessary accuracy over the entire operation period. Thermopile instruments like pyrheliometers as specified in ISO standard 9060 [ISO9060 1990] are severely affected by soiling [Pape2009] and also require expensive and maintenance- intensive support devices such as solar trackers and power supply. Thus, the uncertainty of resource assessment with pyrheliometers depends heavily on the maintenance personnel and cannot be determined accurately in many cases. Due to their low soiling susceptibility, low power demand, and comparatively lower cost, Rotating Shadowband Irradiometers (RSI) show significant dvantages over the thermopile sensors when operated under the measurement conditions of remote weather stations. RSIs are also known as RSP (Rotating Shadowband Pyranometers) or RSR™ (Rotating Shadowband Radiometers). Here we use the notation RSI to refer to either instrument measuring irradiance by use of a rotating shadowband following the decision of the International expert group in IEA Solar Heating and Cooling Task 46, subtask B. The initially lower accuracy of RSIs, which can yield deviations of 5 to 10 % and more, is notably improved with proper calibration of the sensors and corrections of the systematic deviations of its response. Main causes of the systematic deviations are the limited spectral sensitivity and temperature dependence of the Si-photodiode commonly used in most RSIs. Besides the systematic deviations of the sensor response, a significant contribution to the measurement inaccuracy originates from the sensor calibration at the manufacturer, where no corrections are applied. For proper calibration however, the proposed corrections need yet to be considered in the calibration procedure. While well documented standards exist for the calibration of pyrheliometers and pyranometers ([ISO9059 1990], [ISO9846 1993], [ISO9847, 1992]) they cannot be applied to RSIs and no corresponding standards exist for RSIs This document contains RSI specific best practices for the following tasks: - Requirements on the selection of a location for a measurement station - Installation, operation and maintenance of a measurement station, including the case of remote sites - Documentation and quality control of the measurements - Correction of systematic errors & instrument calibration: procedure and frequency Also the performance and accuracy of RSIs are described

Long-term behavior, accuracy and drift of LI-200 pyranometers as radiation sensors in Rotating Shadowband Irradiometers (RSI)

Rotating Shadowband Irradiometers (RSI) are frequently used for solar resource assessment at remote sites due to their significantly higher robustness for soiling, their lower power and maintenance requirements and their cheaper acquisition and operation in contrast to pyrheliometer on tracker systems. The primordial lower accuracy of their photodiode sensor, usually a LI-200 pyranometer from LI-COR Inc., is mainly caused by restrictions of their spectral sensitivity and temperature dependence. However accuracy is notably increased by application of corrections to the raw sensor response. Thus, finally a coincidence of DNI measurements from RSIs with high-precision pyrheliometer measurements within 15 W/m2 (root mean square deviation for 10 min averages) for actual values, less than 3% for daily DNI and within approximately 1.5% of the monthly and annual sum is reached. Within this contribution, the long-term behavior of the LI-COR sensor is examined with regard to the drift of the photodiode sensitivity. This is analyzed from recalibrations of 30 sensors after one to four years and from long-term studies lasting from one to several years. If a significant drift appears, the corresponding uncertainties can be reduced through recalculation of the previous measurement data for the total measurement campaign. Furthermore, studies about the coincidence and deviation of the responses for global, diffuse and direct irradiance of RSI measurements between several individual RSIs and to reference measurements from high-precision thermopiles are presented for different time resolutions